This invention relates to the improvement of feed utilisation and growth in economically important animals, and in particular provides compounds which are useful for improving the efficiency of feed utilisation and/or growth of animals, compositions containing such compounds and a method of improving the efficiency of feed utilisation and/or growth of animals by administering the compounds to the animals.
There is a continuing need throughout the world for animal protein for food. One method of improving the efficiency of production of this is by the use of animal feed additives which improve the utilisation of the ingested feed, thereby producing greater weight gain in the animals in the same period of feeding or from the same amount of ingested feed. Other methods include injection, implantation, or incorporation in the drinking water, or substances which have such an effect.
Thyrotropin releasing hormone (TRH) is a naturally occurring tripeptide identified as L-pyroglutamyl-L-histidyl-L-prolinamide which is present in many species of animals. It is a hypothalamic neurohormone which stimulates the release of thyrotropin from the anterior pituitary gland and which is also known to stimulate the release of growth hormone in certain species, which regulates growth of the animal.
TRH has previously been administered by injection into sheep and cattle in an attempt to improve feed utilisation and growth, and it has also been administered to cows to improve milk production. Also recently described, in published European patent application 0080854, is the use of TRH by oral administration to improve feed utilisation and growth in chickens.
We have now discovered that certain analogues of TRH, in particular wherein the histidyl amino-acid residue is replaced by a pyridylalanyl residue, have much improved growth promoting and/or feed utilisation improving properties which make them valuable for administration to economically important food-source animals such as cattle, sheep, pigs and poultry. Also, by virtue of the involvement of TRH in the stimulation of lactation, the compounds are valuable for improving milk production in cows.